1. Field of the Invention
The invention is related to the art of color measurement. More specifically the invention is related to a method and apparatus for the detection and filtering of transient errors from a signal produced by a color measurement device. The method includes the substitution of a reasonable signal for color measurement signals that are outside reasonable levels. A system model or historical data are used to determine a reasonable signal level for a given color. The invention will be described in reference to a color reprographic environment such as, for example a color xerographic environment. However, the invention is applicable to any environment where color is a useful measure of a process or plant. For example, the invention finds application in monitoring the dying of textiles, plant hydration, food processing and industrial control applications, such as, for example, coil coating.
2. Description of Related Art
In order to provide the best possible color reproduction, reprographic devices have been developed that include color sensors. For example, spectrophotometers have been included in reprographic environments, such as, for example color xerographic environments. The color sensors provide color feedback signals for color control systems. The color control systems use the feedback signals to selectively adjust control parameters and/or color compensation techniques to maintain optimum color reproduction performance.
For example, a color control system may use a color feedback signal to adjust the shape or values associated with a tone reproduction curve (TRC). Tone reproduction curves are known in the art of color reproduction. Tone reproduction curves relate a given color request or input, to an amount of colorant or output signal required to produce the requested color.
In order to maximize a number or percentage of high quality copies produced in a given reproduction run, the color control systems are tuned to respond quickly to system changes reported by the color sensor. As a result, noise or sensor glitches can cause significant control system disturbances. Such disturbances can affect the quality of an unacceptably large number of print job copies. Additionally, unnecessary machine shut downs and service calls are sometimes made in response to the print quality problems resulting from momentary sensor errors.
One solution to this problem is to detune the color control system. Detuning the system would slow system response, thereby reducing the significance of any short-lived color sensor transient. However, detuning the system would also slow system responses to less transient events and perhaps increase following errors in general.
Another solution to this problem might be to add one or more backup or redundant color sensors to the system. For example, a plurality of color sensors, sensing the same color or image portion could be polled. The most reasonable measured color sensor signal could then be treated as the correct or preferred sensor signal. However, this approach has several drawbacks. For example, color sensors are expensive. Additionally, multiple sensors may not fit in a particular system.
Instead of detuning the color control system or installing backup sensors, it is preferable to simply log or count transient errors and to continue printing based on best available information. For example, a system model can be used to temporarily replace the sensor signal. A system shut down and/or service call need only occur if, for example, the transient errors occur at an unacceptably high rate.